Tgf-β1 Inhibits Cftr Biogenesis and Prevents Functional Rescue of ΔF508-Cftr in Primary Differentiated Human Bronchial Epithelial Cells

CFTR is an integral transmembrane glycoprotein and a cAMP-activated Cl2 channel. Mutations in the CFTR gene lead to\ud Cystic Fibrosis (CF)–an autosomal recessive disease with majority of the morbidity and mortality resulting from airway\ud infection, inflammation, and fibrosis. The most common disease-associated mutation in the CFTR gene–deletion of Phe508\ud (DF508) leads to a biosynthetic processing defect of CFTR. Correction of the defect and delivery of DF508-CFTR to the cell\ud surface has been highly anticipated as a disease modifying therapy. Compared to promising results in cultured cell this\ud approach was much less effective in CF patients in an early clinical trial. Although the cause of failure to rescue DF508-CFTR\ud in the clinical trial has not been determined, presence of factor(s) that interfere with the rescue in vivo could be considered.\ud The cytokine TGF-b1 is frequently elevated in CF patients. TGF-b1 has pleiotropic effects in different disease models and\ud genetic backgrounds and little is known about TGF-b1 effects on CFTR in human airway epithelial cells. Moreover, there are\ud no published studies examining TGF-b1 effects on the functional rescue of DF508-CFTR. Here we found that TGF-b1 inhibits\ud CFTR biogenesis by reducing mRNA levels and protein abundance in primary differentiated human bronchial epithelial\ud (HBE) cells from non-CF individuals. TGF-b1 inhibits CFTR biogenesis without compromising the epithelial phenotype or\ud integrity of HBE cells. TGF-b1 also inhibits biogenesis and impairs the functional rescue of DF508-CFTR in HBE cells from\ud patients homozygous for the DF508 mutation. Our data indicate that activation of TGF-b1 signaling may inhibit CFTR\ud function in non-CF individuals and may interfere with therapies directed at correcting the processing defect of DF508-CFTR\ud in CF patients